The reason it's not reproducible is because it happens during some JIT compiling, so it's not really something we can "fix", since the symptom happens almost at random. The reason the try/catch works is because methods with try catch blocks don't get compiled.

Take a look at the Bugzilla report evant mentioned. It looks like Mozilla are still debating whether or not to include a fix in 18.0.1 dependent on 'user feedback'. Anyone who's keen to see this fixed quickly might want to voice their support to Mozilla.

I'd asked for further information about integration state of the patch in the next releases. Unfortunately, the current patch has raised a regression test last night and therefor an automatic pull of the patch.

I give you a quote about the current Mozilla issue 818023:

The change has since been backed out for test regressions (it will be in today's Nightly, but not after that, once the backout merges in later today), however you can test a build with it at: